Method for producing reversible blades

ABSTRACT

The invention relates to a method for producing reversible knives (W) with profiled cross section, in particular for a use in chopping machines for wood chipping, composed in cross section of a proximal support part ( 2 ) with at least one fitting means ( 21, 22 ) for fastening the knife (W) in a detachable and displacement-proof manner and on both sides on the support part ( 2 ) a distal chipping region ( 5 ) containing the cutting edges ( 52 ) , wherein a preliminary material ( 1 ) with large longitudinal extension is subjected to a surface processing ( 11 ) and a support profile ( 2 ) is formed therefrom by rolling. In order to economically optimize the property profile of reversible knives it is provided according to the invention that the distal regions ( 23 ) of the support part ( 2 ), worked in an overfilled rolling groove and having a large longitudinal extension, are removed in passage, respectively forming a bonding surface ( 31 ) axially symmetrically in the longitudinal direction, after which respectively one attachment part ( 4 ) of tool steel is attached to these processed surfaces ( 31 ) of the support part ( 2 ) by means of metallic bonding ( 41 ), and from the attachment parts ( 4 ) chipping regions ( 5 ) with respectively one blade region ( 51 ) and one cutting edge ( 52 ) are shaped by chip removal, on which edge regions ( 5 ) a thermal material treatment and subsequently a cutting to length take place to produce reversible knives (W) ready for operation.

The invention relates to a method for producing reversible knives withprofiled cross section, in particular for a use in chopping machines forwood chipping, composed in cross section of a proximal support part withat least one fitting means for fastening the knife in a detachable anddisplacement-proof manner and on both sides on the support part a distalchipping region containing the cutting edges, wherein a preliminarymaterial with large longitudinal extension is subjected to a surfaceprocessing and a support profile is formed therefrom by rolling.

The prior art includes reversible knives of the type described above indifferent embodiments. The embodiments mainly represent advantageouseconomical and/or technical innovations with respect to a specialproperty profile of the knives.

EP 0 271 481 A, for example, discloses a method for producing inparticular machine blades of hot-rolled flat steel, wherein a roll tabwith homogeneous material structure in the cutting edge region is formedessentially on the side surface by overfilling the last groove.

From DE-OS-27 04 999 a method is known for producing strip-steel knivesin continuous passage, wherein the strip is provided with a centralgroove or flute and the strip is guided on this groove or flute throughthe following work zones.

A reversible knife that can be used in a knife carrier in apredetermined position by projections or recesses interacting in termsof fit, and two welded-on working parts distal in cross section withblades of high-alloy tool steel, is disclosed by document AT 398 401 B.

Flat-steel knives with a rear end part optionally pressed on or a curvedend part for attachment, which is positioned opposite the blade part,formed of tool steel, with a cutting edge are known from US 2009/0217794 A1.

Reversible knives of the referenced type have economical disadvantagesdue to a complex production method and/or disadvantages of inadequateproduct quality or a lack of individual desired use qualities.

The object of the invention is now to disclose a generic method forproducing reversible knives, by means of which the property profilethereof is optimized economically even with harsh stresses in use.

This object is attained with a method of the type mentioned at theoutset in that the distal regions of the support part, worked in anoverfilled rolling groove and having a large longitudinal extension, areremoved in passage, respectively forming a bonding surface axiallysymmetrically in the longitudinal direction, after which respectivelyone attachment part of tool steel is attached to these processedsurfaces of the support part by means of metallic bonding, and from theattachment parts chipping regions with respectively one blade region andone cutting edge are shaped by chip removal, on which edge regions athermal material treatment and subsequently a cutting to length takeplace for reversible knives ready for operation.

The advantages achieved with the method according to the invention areessentially due to the fact that proximal fitting means and distalregions of the support part are simultaneously formed from thepreliminary material by rolling in an overfilled groove, which distalparts far towards the longitudinal axis have a cold-worked, essentiallyunoriented structure and consequently a preferred strengthening of thematerial. These distal hardened parts, partially pressed out of thegroove, are removed essentially at room temperature and a flat surfaceis formed, wherein it is ensured that the strength of the materialachieved by cold working is retained in the flat region.

Attachment parts of tool steel are metallically connected to thesurfaces of the support part formed in this manner, wherein theconnection or welding is carried out in a high-energy manner, that is,without disadvantageous depth action. In this manner only an unimportantreduction in strength of the material of the support part hardened bycold working is achieved in the connection region, which produces adesired high mechanical stability of a fixing of the attachment part.

A forming of a chipping region with a cutting edge takes placerespectively on the attachment part by means of cutting, optionally incombination with partial cold working, wherein a high-strengthconnection to the support part is maintained.

A thermal material hardening and tempering of the edge region is therebyprovided such that no heat affecting of the zone with the metallic bondor welding without any additional materials takes place on theattachment part.

A final sharpening of the blade and a cutting to length of the knivescan now take place in a simple manner.

In one embodiment of the invention it is advantageous if the preliminarymaterial with large longitudinal extension, after a dimensionally exactprocessing of the surface thereof and before a rolling to form a supportpart, is heated by a rapid heating in a period of less than 50 sec., inparticular of less than 15 sec., preferably by means of inductionheating, in passage to a temperature of less than 900° C. with theproviso that the structure of the material remains in a cubicbody-centered atomic structure. In this manner, by means of a directlyupstream dimensionally exact processing of the surface, an exactdimensioning of the preliminary material and thus a precise definitionof the dimensions of the rolled product, on the one hand, and, on theother hand, a high quality non-scaling surface quality of the supportprofile, in particular the adjacent surfaces of the fitting means, takeplace. To avoid a disadvantageous oxide formation, it is advantageousfor the preliminary material to provide a rapid heating in a period ofless than 50 sec., which heating is preferably carried out by inductionin passage. A maximum temperature for shaping the preliminary materialis determined by the chemical composition or by the carbon content ofthe material. For a work hardening of the material during the shaping,at most a temperature is necessary at which a recrystallization of thestructure is avoided and thus a forming of the part takes place in thetemperature range with cubic body-centered atomic structure.

In order to achieve favorable conditions for a connection of theattached parts by fusion welding without any additional material with asmall heat-affected zone, it can be advantageous with respect to a goodadhesion and a precise consistence over the longitudinal extension ifaxially symmetrically distal regions are removed from the shaped supportpart during its guidance by the fitting means in passage with theformation of processed flat surfaces, wherein the width of the surfacesis more than 0.9 mm but less than 2.9 mm.

It is thereby advantageous in terms of bonding technology if with ashift in the longitudinal axial direction and with guidance of thesupport part by the fitting means, this is metallically fixed withattached parts of tool steel with a thickness of more than 0.9 mm butless than 2.9 mm and a width of 1.0 mm to 4 mm by fusion without anyadditional material, in particular by means of laser welding.

Advantageously, the carbon content of the usually low-alloy support partis to be oriented to the carbon activity of the attached partsestablished by alloying technology, in order to keep low or inactive acarbon diffusion to the high-alloy tool steel and thus a danger of aformation of a brittle region in the welding zone.

If the attached parts on the support part are further developed bycutting and/or by non-cutting shaping to form chipping regionsessentially triangular in cross section with cutting edges, themechanical stresses in the region of the connection zone can beminimized in a favorable manner and the material strength therein can beincreased.

Advantageously, the blade regions with the cutting edges on the chippingpart after a final machining to the axially symmetrical preciserepresentation of the cutting edges in passage are subjected to athermal material quenching and tempering by hardening and quenching theblade region of tool steel. In this manner desired properties andhardness values of the blade regions with respect to the field of use ofthe knives can be adjusted. However, it is necessary thereby to restrictthe material quenching and tempering of the tool steel to the bladeregion and to avoid a disadvantageous heating of the chipping part inthe region of the weld seam because an embrittling therein can lead to abreakage of the metallic bond.

It can be favorable for economic reasons if optionally from anintermediate storage a support part with great longitudinal extensionafter shaping of the distal chipping and blade regions and a thermalquenching and tempering of the regions with the dressed cutting edges iscut to length and finally formed to produce reversible knives ready foruse.

The invention is described in more detail below based on drawings whichare intended to illustrate a production process for knives, and onexemplary embodiments, which show only one way of carrying out theinvention.

The graphical representations show

FIG. 1 Preliminary material

FIG. 2 Shaped support part

FIG. 3 Processed support part

FIG. 4 Support part with attached part

FIG. 5 Support part with chipping region

FIG. 6 Reversible knife

FIG. 1 shows a cylindrical preliminary material 1 with a processedsurface 11 with a rough depth R_(y), (R_(z) ISO) of less than 45 μm.

FIG. 2 shows a support profile 2 shaped by means of rolling with anoverfilled groove, which support profile in the distal regionsrespectively has a roll tab 23. During rolling fitting means 21, 22 witha concave shape 21 and a convex 22 shape have been worked proximally atthe same time into the carrier body 2.

FIG. 3 shows diagrammatically a support profile body produced byseparation 3 from the distal roll tabs 23 and provided with processedsurfaces 3.

FIG. 4 shows in a schematic illustration respectively one attached part4 fixed to the support part 2, wherein a metallic bonding 41 of theparts 2, 4 was carried out by fusing without any additional material, inparticular by means of laser welding.

FIG. 5 shows respectively a chipping part 5 formed by processing anattached part 4, with a blade region 51 distanced from a bond or a weldseam 41.

FIG. 6 shows diagrammatically a knife W cut to measured lengthcomprising a support part 2 with proximally positioned fitting means 21,22 comprising a concave indentation 21 shaped in the knife axiallongitudinal direction and a convex projection 22 lying opposite withattached parts 4 permanently attached to the support part 2 distally bymetallic bonding 41, which attached parts are further developed to formchipping parts 5 and have thermally hardened blade regions 51 withcutting edges 52.

By means of practical tests so-called “trimetal” reversible knives of asupport part 2 formed of high carbon steel and a chipping part 5comprising a high-speed steel alloy EN/DIN material no. 1.3247 orAISI-M42 hardened and tempered to a hardness of 65 HRC in the bladeregion were examined and tested practically in a hard insert.

Test results showed that, above a certain carbon content of the supportpart 2 material, a carbon diffusion towards the tool steel part in theconnection region 41 can take place depending on temperature and time,whereby brittle regions formed in the weld seam can cause the chippingparts 5 to break loose.

Support parts 2 of carbon steels with a low C concentration of less than0.35% by weight showed this danger to a much lower extent, wherein aprior strengthening of the material caused by cold working at atemperature in the alpha range of the alloy provides sufficienttoughness and strength properties for extreme stresses of the kniveseven after an attachment by welding of an attached part 4.

1. A method for producing reversible knives (W) with profiled crosssection, in particular for a use in chopping machines for wood chipping,composed in cross section of a proximal support part (2) with at leastone fitting means (21, 22) for fastening the knife (W) in a detachableand displacement-proof manner and on both sides on the support part (2)a distal chipping region (5) containing the cutting edges (52) , whereina preliminary material (1) with large longitudinal extension issubjected to a surface processing (11) and a support profile (2) isformed therefrom by rolling, characterized in that the distal regions(23) of the support part (2), worked in an overfilled rolling groove andhaving a large longitudinal extension, are removed in passage,respectively forming a bonding surface (31) axially symmetrically in thelongitudinal direction, after which respectively one attachment part (4)of tool steel is attached to these processed surfaces (31) of thesupport part (2) by means of metallic bonding (41), and from theattachment parts (4) chipping regions (5) with respectively one bladeregion (51) and one cutting edge (52) are shaped by chip removal and/orcold forming, on which edge regions (5) a thermal material treatment andsubsequently a cutting to length take place for reversible knives (W)ready for operation.
 2. The method according to claim 1, characterizedin that the preliminary material (1) with large longitudinal extension,after a dimensionally exact processing of the surface thereof and beforea rolling to form a support part (2), is heated by a rapid heating in aperiod of less than 50 sec., in particular of less than 15 sec.,preferably by means of induction heating, in passage to a temperature ofless than 900° C. with the proviso that the structure of the materialremains in a cubic body-centered atomic structure.
 3. The methodaccording to claim 1, characterized in that axially symmetrically distalregions are removed from the shaped support part (2) during its guidanceby the fitting means (21, 22) in passage with the formation of processedflat surfaces (31), wherein the width of the surfaces is more than 0.9mm but less than 2.9 mm.
 4. The method according to claim 1,characterized in that with a shift in the longitudinal axial directionand with guidance of the support part (2) by the fitting means (21, 22),this is metallically fixed with attached parts (4) with a thickness ofmore than 0.9 mm but less than 2.9 mm and a width of 1.0 mm to 4 mm,preferably by fusion without any additional material, in particular bymeans of laser welding.
 5. The method according to claim 1,characterized in that the attached parts (4) are further developed bycutting and/or by non-cutting shaping to form chipping regions (5)essentially triangular in cross section with cutting edges (52).
 6. Themethod according to claim 1, characterized in that the blade regions(51) with the cutting edges (52) on the chipping region (5) of thesupport part (2) after a final machining to the axially symmetricalrepresentation of the cutting edges (52) in passage are subjected to amaterial heat treating by quenching and tempering the blade region (51)of tool steel.
 7. The method according to claim 1, characterized in thata support part (2) with great longitudinal extension after shaping ofthe distal chipping and blade regions (5, 51) and a thermal quenchingand tempering of the dressed cutting edges (52) is cut to length andfinally formed to produce reversible knives ready for use.